COCA (Collaborative Objects Coordination Architecture) was proposed as a novel means to model and support collaborations over the Internet. Our approach separates coordination policies from user interfaces and the pol...
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ISBN:
(纸本)1581132557
COCA (Collaborative Objects Coordination Architecture) was proposed as a novel means to model and support collaborations over the Internet. Our approach separates coordination policies from user interfaces and the policies are specified in a logic-based language. Over the past year, both the collaboration model and the specification language have been substantially refined and evaluated through our experience in building real-life collaboration systems. This paper presents the design of the specification language and illustrates the main ideas with a few simple design examples. Semantics, implementation, runtime support, and applications are also covered but not as the focus of this paper.
Java class files are often distributed as jar files, which are collections of individually compressed class files (and possibility other files). Jar files are typically about 1/2 the size of the original class files d...
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Java class files are often distributed as jar files, which are collections of individually compressed class files (and possibility other files). Jar files are typically about 1/2 the size of the original class files due to compression. I have developed a wire-code format for collections of Java class files. This format is typically 1/2 to 1/5 of the size of the corresponding compressed jar file (1/4 to 1/10 the size of the original class files).
Some modern superscalar microprocessors provide only imprecise exceptions. That is, they do not guarantee to report the same exception that would be encountered by a straightforward sequential execution of the program...
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Some modern superscalar microprocessors provide only imprecise exceptions. That is, they do not guarantee to report the same exception that would be encountered by a straightforward sequential execution of the program. In exchange, they offer increased performance or decreased chip area (which amount to much the same thing). This performance/precision tradeoff has not so far been much explored at the programminglanguage level. In this paper we propose a design for imprecise exceptions in the lazy functional programminglanguage Haskell. We discuss several designs, and conclude that imprecision is essential if the language is still to enjoy its current rich algebra of transformations. We sketch a precise semantics for the language extended with exceptions. The paper shows how to extend Haskell with exceptions without crippling the language or its compilers. We do not yet have enough experience of using the new mechanism to know whether it strikes an appropriate balance between expressiveness and performance.
We describe a framework for adding type qualifiers to a language. Type qualifiers encode a simple but highly useful form of subtyping. Our framework extends standard type rules to model the flow of qualifiers through ...
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We describe a framework for adding type qualifiers to a language. Type qualifiers encode a simple but highly useful form of subtyping. Our framework extends standard type rules to model the flow of qualifiers through a program, where each qualifier or set of qualifiers comes with additional rules that capture its semantics. Our framework allows types to be polymorphic in the type qualifiers. We present a const-inference system for C as an example application of the framework. We show that for a set of real C programs, many more consts can be used than are actually present in the original code.
This paper presents a novel interprocedural, flow-sensitive, and context-sensitive pointer analysis algorithm for multi-threaded programs that may concurrently update shared pointers. For each pointer and each program...
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This paper presents a novel interprocedural, flow-sensitive, and context-sensitive pointer analysis algorithm for multi-threaded programs that may concurrently update shared pointers. For each pointer and each program point, the algorithm computes a conservative approximation of the memory locations to which that pointer may point. The algorithm correctly handles a full range of constructs in multi-threaded programs, including recursive functions, function pointers, structures, arrays, nested structures and arrays, pointer arithmetic, casts between pointer variables of different types, heap and stack allocated memory, shared global variables, and thread-private global variables. We have implemented the algorithm in the SUIF compiler system and used the implementation to analyze a sizable set of multithreaded programs written in the Cilk multi-threaded programminglanguage. Our experimental results show that the analysis has good precision and converges quickly for our set of Cilk programs.
Typical class-based languages, such as C++ and JAVA, provide complex class mechanisms but only weak module systems. In fact, classes in these languages incorporate many of the features found in richer module mechanism...
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Typical class-based languages, such as C++ and JAVA, provide complex class mechanisms but only weak module systems. In fact, classes in these languages incorporate many of the features found in richer module mechanisms. In this paper, we describe an alternative approach to designing a language that has both classes and modules. In our design, we rely on a rich ML-style module system to provide features such as visibility control and parameterization, while providing a minimal class mechanism that includes only those features needed to support inheritance. Programmers can then use the combination of modules and classes to implement the full range of class-based features and idioms. Our approach has the advantage that it provides a full-featured module system (useful in its own right), while keeping the class mechanism quite simple. We have incorporated this design in MOBY, which is an ML-style language that supports class-based object-oriented programming. In this paper, we describe our design via a series of simple examples, show how various class-based features and idioms are realized in MOBY, compare our design with others, and sketch its formal semantics.
A hierarchical module system is an effective tool for structuring large programs. Strictly hierarchical module systems impose an acyclic ordering on import dependencies among program units. This can impede modular pro...
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A hierarchical module system is an effective tool for structuring large programs. Strictly hierarchical module systems impose an acyclic ordering on import dependencies among program units. This can impede modular programming by forcing mutually-dependent components to be consolidated into a single module. Recently there have been several proposals for module systems that admit cyclic dependencies, but it is not clear how these proposals relate to one another, nor how one might integrate them into an expressive module system such as that of ML. To address this question we provide a type-theoretic analysis of the notion of a recursive module in the context of a `phase-distinction' formalism for higher-order module systems. We extend this calculus with a recursive module mechanism and a new form of signature, called a recursively dependent signature, to support the definition of recursive modules. These extensions are justified by an interpretation in terms of more primitive language constructs. This interpretation may also serve as a guide for implementation.
The challenge of exploiting high degrees of instruction-level parallelism is often hampered by frequent branching. Both exposed branch latency and low branch throughput can restrict parallelism. Control critical path ...
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The challenge of exploiting high degrees of instruction-level parallelism is often hampered by frequent branching. Both exposed branch latency and low branch throughput can restrict parallelism. Control critical path reduction (control CPR) is a compilation technique to address these problems. Control CPR can reduce the dependence height of critical paths through branch operations as well as decrease the number of executed branches. In this paper, we present an approach to control CPR that recognizes sequences of branches using profiling statistics. The control CPR transformation is applied to the predominant path through this sequence. Our approach, its implementation, and experimental results are presented. This work demonstrates that control CPR enhances instruction-level parallelism for a variety of application programs and improves their performance across a range of processors.
Static Single Assignment (SSA) is an effective intermediate representation in optimizing compilers. However, traditional SSA form and optimizations are not applicable to programs represented as native machine instruct...
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Static Single Assignment (SSA) is an effective intermediate representation in optimizing compilers. However, traditional SSA form and optimizations are not applicable to programs represented as native machine instructions because the use of dedicated registers imposed by calling conventions, the runtime system, and target architecture must be made explicit. We present a simple scheme for converting between programs in machine code and in SSA, such that references to dedicated physical registers in machine code are preserved. Our scheme ignores all output- and anti-dependences imposed by physical registers while a program is in SSA form, but inserts compensation code during machine code reconstruction if any naming requirements have been violated. By resolving all mismatches between the two representations in separate phases, we are able to utilize existing SSA algorithms unaltered to perform machine code optimizations.
Type casting allows a program to access an object as if it had a type different from its declared type. This complicates the design of a pointer-analysis algorithm that treats structure fields as separate objects;ther...
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Type casting allows a program to access an object as if it had a type different from its declared type. This complicates the design of a pointer-analysis algorithm that treats structure fields as separate objects;therefore, some previous pointer-analysis algorithms `collapse' a structure into a single variable. The disadvantage of this approach is that it can lead to very imprecise points-to information. Other algorithms treat each field as a separate object based on its offset and size. While this approach leads to more precise results, the results are not portable because the memory layout of structures is implementation dependent. This paper first describes the complications introduced by type casting, then presents a tunable pointer-analysis framework for handling structures in the presence of casting. Different instances of this framework produce algorithms with different levels of precision, portability, and efficiency. Experimental results from running our implementations of four instances of this framework show that (i) it is important to distinguish fields of structures in pointer analysis, but (ii) making conservative approximations when casting is involved usually does not cost much in terms of time, space, or the precision of the results.
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